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llvm-project/lld/ELF/SyntheticSections.cpp

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//===- SyntheticSections.cpp ----------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains linker-synthesized sections. Currently,
// synthetic sections are created either output sections or input sections,
// but we are rewriting code so that all synthetic sections are created as
// input sections.
//
//===----------------------------------------------------------------------===//
#include "SyntheticSections.h"
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "LinkerScript.h"
#include "Memory.h"
#include "OutputSections.h"
#include "Strings.h"
#include "SymbolTable.h"
#include "Target.h"
#include "Threads.h"
#include "Writer.h"
#include "lld/Config/Version.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
#include "llvm/Object/Decompressor.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/MD5.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/SHA1.h"
#include "llvm/Support/xxhash.h"
#include <cstdlib>
using namespace llvm;
using namespace llvm::dwarf;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::support;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;
uint64_t SyntheticSection::getVA() const {
if (OutputSection *Sec = getParent())
return Sec->Addr + OutSecOff;
return 0;
}
template <class ELFT> static std::vector<DefinedCommon *> getCommonSymbols() {
std::vector<DefinedCommon *> V;
for (Symbol *S : Symtab->getSymbols())
if (auto *B = dyn_cast<DefinedCommon>(S->body()))
V.push_back(B);
return V;
}
// Find all common symbols and allocate space for them.
template <class ELFT> InputSection *elf::createCommonSection() {
if (!Config->DefineCommon)
return nullptr;
// Sort the common symbols by alignment as an heuristic to pack them better.
std::vector<DefinedCommon *> Syms = getCommonSymbols<ELFT>();
if (Syms.empty())
return nullptr;
std::stable_sort(Syms.begin(), Syms.end(),
[](const DefinedCommon *A, const DefinedCommon *B) {
return A->Alignment > B->Alignment;
});
// Allocate space for common symbols.
BssSection *Sec = make<BssSection>("COMMON");
for (DefinedCommon *Sym : Syms)
if (Sym->Live)
Sym->Offset = Sec->reserveSpace(Sym->Size, Sym->Alignment);
return Sec;
}
// Returns an LLD version string.
static ArrayRef<uint8_t> getVersion() {
// Check LLD_VERSION first for ease of testing.
// You can get consitent output by using the environment variable.
// This is only for testing.
StringRef S = getenv("LLD_VERSION");
if (S.empty())
S = Saver.save(Twine("Linker: ") + getLLDVersion());
// +1 to include the terminating '\0'.
return {(const uint8_t *)S.data(), S.size() + 1};
}
// Creates a .comment section containing LLD version info.
// With this feature, you can identify LLD-generated binaries easily
// by "readelf --string-dump .comment <file>".
// The returned object is a mergeable string section.
template <class ELFT> MergeInputSection *elf::createCommentSection() {
typename ELFT::Shdr Hdr = {};
Hdr.sh_flags = SHF_MERGE | SHF_STRINGS;
Hdr.sh_type = SHT_PROGBITS;
Hdr.sh_entsize = 1;
Hdr.sh_addralign = 1;
auto *Ret =
make<MergeInputSection>((ObjFile<ELFT> *)nullptr, &Hdr, ".comment");
Ret->Data = getVersion();
Ret->splitIntoPieces();
return Ret;
}
// .MIPS.abiflags section.
template <class ELFT>
MipsAbiFlagsSection<ELFT>::MipsAbiFlagsSection(Elf_Mips_ABIFlags Flags)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_ABIFLAGS, 8, ".MIPS.abiflags"),
Flags(Flags) {
this->Entsize = sizeof(Elf_Mips_ABIFlags);
}
template <class ELFT> void MipsAbiFlagsSection<ELFT>::writeTo(uint8_t *Buf) {
memcpy(Buf, &Flags, sizeof(Flags));
}
template <class ELFT>
MipsAbiFlagsSection<ELFT> *MipsAbiFlagsSection<ELFT>::create() {
Elf_Mips_ABIFlags Flags = {};
bool Create = false;
for (InputSectionBase *Sec : InputSections) {
if (Sec->Type != SHT_MIPS_ABIFLAGS)
continue;
Sec->Live = false;
Create = true;
std::string Filename = toString(Sec->getFile<ELFT>());
const size_t Size = Sec->Data.size();
// Older version of BFD (such as the default FreeBSD linker) concatenate
// .MIPS.abiflags instead of merging. To allow for this case (or potential
// zero padding) we ignore everything after the first Elf_Mips_ABIFlags
if (Size < sizeof(Elf_Mips_ABIFlags)) {
error(Filename + ": invalid size of .MIPS.abiflags section: got " +
Twine(Size) + " instead of " + Twine(sizeof(Elf_Mips_ABIFlags)));
return nullptr;
}
auto *S = reinterpret_cast<const Elf_Mips_ABIFlags *>(Sec->Data.data());
if (S->version != 0) {
error(Filename + ": unexpected .MIPS.abiflags version " +
Twine(S->version));
return nullptr;
}
// LLD checks ISA compatibility in getMipsEFlags(). Here we just
// select the highest number of ISA/Rev/Ext.
Flags.isa_level = std::max(Flags.isa_level, S->isa_level);
Flags.isa_rev = std::max(Flags.isa_rev, S->isa_rev);
Flags.isa_ext = std::max(Flags.isa_ext, S->isa_ext);
Flags.gpr_size = std::max(Flags.gpr_size, S->gpr_size);
Flags.cpr1_size = std::max(Flags.cpr1_size, S->cpr1_size);
Flags.cpr2_size = std::max(Flags.cpr2_size, S->cpr2_size);
Flags.ases |= S->ases;
Flags.flags1 |= S->flags1;
Flags.flags2 |= S->flags2;
Flags.fp_abi = elf::getMipsFpAbiFlag(Flags.fp_abi, S->fp_abi, Filename);
};
if (Create)
return make<MipsAbiFlagsSection<ELFT>>(Flags);
return nullptr;
}
// .MIPS.options section.
template <class ELFT>
MipsOptionsSection<ELFT>::MipsOptionsSection(Elf_Mips_RegInfo Reginfo)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_OPTIONS, 8, ".MIPS.options"),
Reginfo(Reginfo) {
this->Entsize = sizeof(Elf_Mips_Options) + sizeof(Elf_Mips_RegInfo);
}
template <class ELFT> void MipsOptionsSection<ELFT>::writeTo(uint8_t *Buf) {
auto *Options = reinterpret_cast<Elf_Mips_Options *>(Buf);
Options->kind = ODK_REGINFO;
Options->size = getSize();
if (!Config->Relocatable)
Reginfo.ri_gp_value = InX::MipsGot->getGp();
memcpy(Buf + sizeof(Elf_Mips_Options), &Reginfo, sizeof(Reginfo));
}
template <class ELFT>
MipsOptionsSection<ELFT> *MipsOptionsSection<ELFT>::create() {
// N64 ABI only.
if (!ELFT::Is64Bits)
return nullptr;
Elf_Mips_RegInfo Reginfo = {};
bool Create = false;
for (InputSectionBase *Sec : InputSections) {
if (Sec->Type != SHT_MIPS_OPTIONS)
continue;
Sec->Live = false;
Create = true;
std::string Filename = toString(Sec->getFile<ELFT>());
ArrayRef<uint8_t> D = Sec->Data;
while (!D.empty()) {
if (D.size() < sizeof(Elf_Mips_Options)) {
error(Filename + ": invalid size of .MIPS.options section");
break;
}
auto *Opt = reinterpret_cast<const Elf_Mips_Options *>(D.data());
if (Opt->kind == ODK_REGINFO) {
if (Config->Relocatable && Opt->getRegInfo().ri_gp_value)
error(Filename + ": unsupported non-zero ri_gp_value");
Reginfo.ri_gprmask |= Opt->getRegInfo().ri_gprmask;
Sec->getFile<ELFT>()->MipsGp0 = Opt->getRegInfo().ri_gp_value;
break;
}
if (!Opt->size)
fatal(Filename + ": zero option descriptor size");
D = D.slice(Opt->size);
}
};
if (Create)
return make<MipsOptionsSection<ELFT>>(Reginfo);
return nullptr;
}
// MIPS .reginfo section.
template <class ELFT>
MipsReginfoSection<ELFT>::MipsReginfoSection(Elf_Mips_RegInfo Reginfo)
: SyntheticSection(SHF_ALLOC, SHT_MIPS_REGINFO, 4, ".reginfo"),
Reginfo(Reginfo) {
this->Entsize = sizeof(Elf_Mips_RegInfo);
}
template <class ELFT> void MipsReginfoSection<ELFT>::writeTo(uint8_t *Buf) {
if (!Config->Relocatable)
Reginfo.ri_gp_value = InX::MipsGot->getGp();
memcpy(Buf, &Reginfo, sizeof(Reginfo));
}
template <class ELFT>
MipsReginfoSection<ELFT> *MipsReginfoSection<ELFT>::create() {
// Section should be alive for O32 and N32 ABIs only.
if (ELFT::Is64Bits)
return nullptr;
Elf_Mips_RegInfo Reginfo = {};
bool Create = false;
for (InputSectionBase *Sec : InputSections) {
if (Sec->Type != SHT_MIPS_REGINFO)
continue;
Sec->Live = false;
Create = true;
if (Sec->Data.size() != sizeof(Elf_Mips_RegInfo)) {
error(toString(Sec->getFile<ELFT>()) +
": invalid size of .reginfo section");
return nullptr;
}
auto *R = reinterpret_cast<const Elf_Mips_RegInfo *>(Sec->Data.data());
if (Config->Relocatable && R->ri_gp_value)
error(toString(Sec->getFile<ELFT>()) +
": unsupported non-zero ri_gp_value");
Reginfo.ri_gprmask |= R->ri_gprmask;
Sec->getFile<ELFT>()->MipsGp0 = R->ri_gp_value;
};
if (Create)
return make<MipsReginfoSection<ELFT>>(Reginfo);
return nullptr;
}
InputSection *elf::createInterpSection() {
// StringSaver guarantees that the returned string ends with '\0'.
StringRef S = Saver.save(Config->DynamicLinker);
ArrayRef<uint8_t> Contents = {(const uint8_t *)S.data(), S.size() + 1};
auto *Sec =
make<InputSection>(SHF_ALLOC, SHT_PROGBITS, 1, Contents, ".interp");
Sec->Live = true;
return Sec;
}
SymbolBody *elf::addSyntheticLocal(StringRef Name, uint8_t Type, uint64_t Value,
uint64_t Size, InputSectionBase *Section) {
auto *S = make<DefinedRegular>(Name, /*IsLocal*/ true, STV_DEFAULT, Type,
Value, Size, Section);
if (InX::SymTab)
InX::SymTab->addSymbol(S);
return S;
}
static size_t getHashSize() {
switch (Config->BuildId) {
case BuildIdKind::Fast:
return 8;
case BuildIdKind::Md5:
case BuildIdKind::Uuid:
return 16;
case BuildIdKind::Sha1:
return 20;
case BuildIdKind::Hexstring:
return Config->BuildIdVector.size();
default:
llvm_unreachable("unknown BuildIdKind");
}
}
BuildIdSection::BuildIdSection()
: SyntheticSection(SHF_ALLOC, SHT_NOTE, 1, ".note.gnu.build-id"),
HashSize(getHashSize()) {}
void BuildIdSection::writeTo(uint8_t *Buf) {
endianness E = Config->Endianness;
write32(Buf, 4, E); // Name size
write32(Buf + 4, HashSize, E); // Content size
write32(Buf + 8, NT_GNU_BUILD_ID, E); // Type
memcpy(Buf + 12, "GNU", 4); // Name string
HashBuf = Buf + 16;
}
// Split one uint8 array into small pieces of uint8 arrays.
static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> Arr,
size_t ChunkSize) {
std::vector<ArrayRef<uint8_t>> Ret;
while (Arr.size() > ChunkSize) {
Ret.push_back(Arr.take_front(ChunkSize));
Arr = Arr.drop_front(ChunkSize);
}
if (!Arr.empty())
Ret.push_back(Arr);
return Ret;
}
// Computes a hash value of Data using a given hash function.
// In order to utilize multiple cores, we first split data into 1MB
// chunks, compute a hash for each chunk, and then compute a hash value
// of the hash values.
void BuildIdSection::computeHash(
llvm::ArrayRef<uint8_t> Data,
std::function<void(uint8_t *Dest, ArrayRef<uint8_t> Arr)> HashFn) {
std::vector<ArrayRef<uint8_t>> Chunks = split(Data, 1024 * 1024);
std::vector<uint8_t> Hashes(Chunks.size() * HashSize);
// Compute hash values.
parallelForEachN(0, Chunks.size(), [&](size_t I) {
HashFn(Hashes.data() + I * HashSize, Chunks[I]);
});
// Write to the final output buffer.
HashFn(HashBuf, Hashes);
}
BssSection::BssSection(StringRef Name)
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_NOBITS, 0, Name) {}
size_t BssSection::reserveSpace(uint64_t Size, uint32_t Alignment) {
if (OutputSection *Sec = getParent())
Sec->updateAlignment(Alignment);
this->Size = alignTo(this->Size, Alignment) + Size;
this->Alignment = std::max(this->Alignment, Alignment);
return this->Size - Size;
}
void BuildIdSection::writeBuildId(ArrayRef<uint8_t> Buf) {
switch (Config->BuildId) {
case BuildIdKind::Fast:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
write64le(Dest, xxHash64(toStringRef(Arr)));
});
break;
case BuildIdKind::Md5:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
memcpy(Dest, MD5::hash(Arr).data(), 16);
});
break;
case BuildIdKind::Sha1:
computeHash(Buf, [](uint8_t *Dest, ArrayRef<uint8_t> Arr) {
memcpy(Dest, SHA1::hash(Arr).data(), 20);
});
break;
case BuildIdKind::Uuid:
if (getRandomBytes(HashBuf, HashSize))
error("entropy source failure");
break;
case BuildIdKind::Hexstring:
memcpy(HashBuf, Config->BuildIdVector.data(), Config->BuildIdVector.size());
break;
default:
llvm_unreachable("unknown BuildIdKind");
}
}
template <class ELFT>
EhFrameSection<ELFT>::EhFrameSection()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame") {}
// Search for an existing CIE record or create a new one.
// CIE records from input object files are uniquified by their contents
// and where their relocations point to.
template <class ELFT>
template <class RelTy>
CieRecord *EhFrameSection<ELFT>::addCie(EhSectionPiece &Piece,
ArrayRef<RelTy> Rels) {
auto *Sec = cast<EhInputSection>(Piece.ID);
const endianness E = ELFT::TargetEndianness;
if (read32<E>(Piece.data().data() + 4) != 0)
fatal(toString(Sec) + ": CIE expected at beginning of .eh_frame");
SymbolBody *Personality = nullptr;
unsigned FirstRelI = Piece.FirstRelocation;
if (FirstRelI != (unsigned)-1)
Personality =
&Sec->template getFile<ELFT>()->getRelocTargetSym(Rels[FirstRelI]);
// Search for an existing CIE by CIE contents/relocation target pair.
CieRecord *Cie = &CieMap[{Piece.data(), Personality}];
// If not found, create a new one.
if (Cie->Piece == nullptr) {
Cie->Piece = &Piece;
Cies.push_back(Cie);
}
return Cie;
}
// There is one FDE per function. Returns true if a given FDE
// points to a live function.
template <class ELFT>
template <class RelTy>
bool EhFrameSection<ELFT>::isFdeLive(EhSectionPiece &Piece,
ArrayRef<RelTy> Rels) {
auto *Sec = cast<EhInputSection>(Piece.ID);
unsigned FirstRelI = Piece.FirstRelocation;
if (FirstRelI == (unsigned)-1)
return false;
const RelTy &Rel = Rels[FirstRelI];
SymbolBody &B = Sec->template getFile<ELFT>()->getRelocTargetSym(Rel);
auto *D = dyn_cast<DefinedRegular>(&B);
if (!D || !D->Section)
return false;
auto *Target =
cast<InputSectionBase>(cast<InputSectionBase>(D->Section)->Repl);
return Target && Target->Live;
}
// .eh_frame is a sequence of CIE or FDE records. In general, there
// is one CIE record per input object file which is followed by
// a list of FDEs. This function searches an existing CIE or create a new
// one and associates FDEs to the CIE.
template <class ELFT>
template <class RelTy>
void EhFrameSection<ELFT>::addSectionAux(EhInputSection *Sec,
ArrayRef<RelTy> Rels) {
const endianness E = ELFT::TargetEndianness;
DenseMap<size_t, CieRecord *> OffsetToCie;
for (EhSectionPiece &Piece : Sec->Pieces) {
// The empty record is the end marker.
if (Piece.size() == 4)
return;
size_t Offset = Piece.InputOff;
uint32_t ID = read32<E>(Piece.data().data() + 4);
if (ID == 0) {
OffsetToCie[Offset] = addCie(Piece, Rels);
continue;
}
uint32_t CieOffset = Offset + 4 - ID;
CieRecord *Cie = OffsetToCie[CieOffset];
if (!Cie)
fatal(toString(Sec) + ": invalid CIE reference");
if (!isFdeLive(Piece, Rels))
continue;
Cie->FdePieces.push_back(&Piece);
NumFdes++;
}
}
template <class ELFT>
void EhFrameSection<ELFT>::addSection(InputSectionBase *C) {
auto *Sec = cast<EhInputSection>(C);
Sec->Parent = this;
updateAlignment(Sec->Alignment);
Sections.push_back(Sec);
for (auto *DS : Sec->DependentSections)
DependentSections.push_back(DS);
// .eh_frame is a sequence of CIE or FDE records. This function
// splits it into pieces so that we can call
// SplitInputSection::getSectionPiece on the section.
Sec->split<ELFT>();
if (Sec->Pieces.empty())
return;
if (Sec->NumRelocations) {
if (Sec->AreRelocsRela)
addSectionAux(Sec, Sec->template relas<ELFT>());
else
addSectionAux(Sec, Sec->template rels<ELFT>());
return;
}
addSectionAux(Sec, makeArrayRef<Elf_Rela>(nullptr, nullptr));
}
template <class ELFT>
static void writeCieFde(uint8_t *Buf, ArrayRef<uint8_t> D) {
memcpy(Buf, D.data(), D.size());
// Fix the size field. -4 since size does not include the size field itself.
const endianness E = ELFT::TargetEndianness;
write32<E>(Buf, alignTo(D.size(), sizeof(typename ELFT::uint)) - 4);
}
template <class ELFT> void EhFrameSection<ELFT>::finalizeContents() {
if (this->Size)
return; // Already finalized.
size_t Off = 0;
for (CieRecord *Cie : Cies) {
Cie->Piece->OutputOff = Off;
Off += alignTo(Cie->Piece->size(), Config->Wordsize);
for (EhSectionPiece *Fde : Cie->FdePieces) {
Fde->OutputOff = Off;
Off += alignTo(Fde->size(), Config->Wordsize);
}
}
// The LSB standard does not allow a .eh_frame section with zero
// Call Frame Information records. Therefore add a CIE record length
// 0 as a terminator if this .eh_frame section is empty.
if (Off == 0)
Off = 4;
this->Size = Off;
}
template <class ELFT> static uint64_t readFdeAddr(uint8_t *Buf, int Size) {
const endianness E = ELFT::TargetEndianness;
switch (Size) {
case DW_EH_PE_udata2:
return read16<E>(Buf);
case DW_EH_PE_udata4:
return read32<E>(Buf);
case DW_EH_PE_udata8:
return read64<E>(Buf);
case DW_EH_PE_absptr:
if (ELFT::Is64Bits)
return read64<E>(Buf);
return read32<E>(Buf);
}
fatal("unknown FDE size encoding");
}
// Returns the VA to which a given FDE (on a mmap'ed buffer) is applied to.
// We need it to create .eh_frame_hdr section.
template <class ELFT>
uint64_t EhFrameSection<ELFT>::getFdePc(uint8_t *Buf, size_t FdeOff,
uint8_t Enc) {
// The starting address to which this FDE applies is
// stored at FDE + 8 byte.
size_t Off = FdeOff + 8;
uint64_t Addr = readFdeAddr<ELFT>(Buf + Off, Enc & 0x7);
if ((Enc & 0x70) == DW_EH_PE_absptr)
return Addr;
if ((Enc & 0x70) == DW_EH_PE_pcrel)
return Addr + getParent()->Addr + Off;
fatal("unknown FDE size relative encoding");
}
template <class ELFT> void EhFrameSection<ELFT>::writeTo(uint8_t *Buf) {
const endianness E = ELFT::TargetEndianness;
for (CieRecord *Cie : Cies) {
size_t CieOffset = Cie->Piece->OutputOff;
writeCieFde<ELFT>(Buf + CieOffset, Cie->Piece->data());
for (EhSectionPiece *Fde : Cie->FdePieces) {
size_t Off = Fde->OutputOff;
writeCieFde<ELFT>(Buf + Off, Fde->data());
// FDE's second word should have the offset to an associated CIE.
// Write it.
write32<E>(Buf + Off + 4, Off + 4 - CieOffset);
}
}
for (EhInputSection *S : Sections)
S->relocateAlloc(Buf, nullptr);
// Construct .eh_frame_hdr. .eh_frame_hdr is a binary search table
// to get a FDE from an address to which FDE is applied. So here
// we obtain two addresses and pass them to EhFrameHdr object.
if (In<ELFT>::EhFrameHdr) {
for (CieRecord *Cie : Cies) {
uint8_t Enc = getFdeEncoding<ELFT>(Cie->Piece);
for (SectionPiece *Fde : Cie->FdePieces) {
uint64_t Pc = getFdePc(Buf, Fde->OutputOff, Enc);
uint64_t FdeVA = getParent()->Addr + Fde->OutputOff;
In<ELFT>::EhFrameHdr->addFde(Pc, FdeVA);
}
}
}
}
GotSection::GotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotEntrySize, ".got") {}
void GotSection::addEntry(SymbolBody &Sym) {
Sym.GotIndex = NumEntries;
++NumEntries;
}
bool GotSection::addDynTlsEntry(SymbolBody &Sym) {
if (Sym.GlobalDynIndex != -1U)
return false;
Sym.GlobalDynIndex = NumEntries;
// Global Dynamic TLS entries take two GOT slots.
NumEntries += 2;
return true;
}
// Reserves TLS entries for a TLS module ID and a TLS block offset.
// In total it takes two GOT slots.
bool GotSection::addTlsIndex() {
if (TlsIndexOff != uint32_t(-1))
return false;
TlsIndexOff = NumEntries * Config->Wordsize;
NumEntries += 2;
return true;
}
uint64_t GotSection::getGlobalDynAddr(const SymbolBody &B) const {
return this->getVA() + B.GlobalDynIndex * Config->Wordsize;
}
uint64_t GotSection::getGlobalDynOffset(const SymbolBody &B) const {
return B.GlobalDynIndex * Config->Wordsize;
}
void GotSection::finalizeContents() { Size = NumEntries * Config->Wordsize; }
bool GotSection::empty() const {
// If we have a relocation that is relative to GOT (such as GOTOFFREL),
// we need to emit a GOT even if it's empty.
return NumEntries == 0 && !HasGotOffRel;
}
void GotSection::writeTo(uint8_t *Buf) {
// Buf points to the start of this section's buffer,
// whereas InputSectionBase::relocateAlloc() expects its argument
// to point to the start of the output section.
relocateAlloc(Buf - OutSecOff, Buf - OutSecOff + Size);
}
MipsGotSection::MipsGotSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE | SHF_MIPS_GPREL, SHT_PROGBITS, 16,
".got") {}
void MipsGotSection::addEntry(SymbolBody &Sym, int64_t Addend, RelExpr Expr) {
// For "true" local symbols which can be referenced from the same module
// only compiler creates two instructions for address loading:
//
// lw $8, 0($gp) # R_MIPS_GOT16
// addi $8, $8, 0 # R_MIPS_LO16
//
// The first instruction loads high 16 bits of the symbol address while
// the second adds an offset. That allows to reduce number of required
// GOT entries because only one global offset table entry is necessary
// for every 64 KBytes of local data. So for local symbols we need to
// allocate number of GOT entries to hold all required "page" addresses.
//
// All global symbols (hidden and regular) considered by compiler uniformly.
// It always generates a single `lw` instruction and R_MIPS_GOT16 relocation
// to load address of the symbol. So for each such symbol we need to
// allocate dedicated GOT entry to store its address.
//
// If a symbol is preemptible we need help of dynamic linker to get its
// final address. The corresponding GOT entries are allocated in the
// "global" part of GOT. Entries for non preemptible global symbol allocated
// in the "local" part of GOT.
//
// See "Global Offset Table" in Chapter 5:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Expr == R_MIPS_GOT_LOCAL_PAGE) {
// At this point we do not know final symbol value so to reduce number
// of allocated GOT entries do the following trick. Save all output
// sections referenced by GOT relocations. Then later in the `finalize`
// method calculate number of "pages" required to cover all saved output
// section and allocate appropriate number of GOT entries.
PageIndexMap.insert({Sym.getOutputSection(), 0});
return;
}
if (Sym.isTls()) {
// GOT entries created for MIPS TLS relocations behave like
// almost GOT entries from other ABIs. They go to the end
// of the global offset table.
Sym.GotIndex = TlsEntries.size();
TlsEntries.push_back(&Sym);
return;
}
auto AddEntry = [&](SymbolBody &S, uint64_t A, GotEntries &Items) {
if (S.isInGot() && !A)
return;
size_t NewIndex = Items.size();
if (!EntryIndexMap.insert({{&S, A}, NewIndex}).second)
return;
Items.emplace_back(&S, A);
if (!A)
S.GotIndex = NewIndex;
};
if (Sym.isPreemptible()) {
// Ignore addends for preemptible symbols. They got single GOT entry anyway.
AddEntry(Sym, 0, GlobalEntries);
Sym.IsInGlobalMipsGot = true;
} else if (Expr == R_MIPS_GOT_OFF32) {
AddEntry(Sym, Addend, LocalEntries32);
Sym.Is32BitMipsGot = true;
} else {
// Hold local GOT entries accessed via a 16-bit index separately.
// That allows to write them in the beginning of the GOT and keep
// their indexes as less as possible to escape relocation's overflow.
AddEntry(Sym, Addend, LocalEntries);
}
}
bool MipsGotSection::addDynTlsEntry(SymbolBody &Sym) {
if (Sym.GlobalDynIndex != -1U)
return false;
Sym.GlobalDynIndex = TlsEntries.size();
// Global Dynamic TLS entries take two GOT slots.
TlsEntries.push_back(nullptr);
TlsEntries.push_back(&Sym);
return true;
}
// Reserves TLS entries for a TLS module ID and a TLS block offset.
// In total it takes two GOT slots.
bool MipsGotSection::addTlsIndex() {
if (TlsIndexOff != uint32_t(-1))
return false;
TlsIndexOff = TlsEntries.size() * Config->Wordsize;
TlsEntries.push_back(nullptr);
TlsEntries.push_back(nullptr);
return true;
}
static uint64_t getMipsPageAddr(uint64_t Addr) {
return (Addr + 0x8000) & ~0xffff;
}
static uint64_t getMipsPageCount(uint64_t Size) {
return (Size + 0xfffe) / 0xffff + 1;
}
uint64_t MipsGotSection::getPageEntryOffset(const SymbolBody &B,
int64_t Addend) const {
const OutputSection *OutSec = B.getOutputSection();
uint64_t SecAddr = getMipsPageAddr(OutSec->Addr);
uint64_t SymAddr = getMipsPageAddr(B.getVA(Addend));
uint64_t Index = PageIndexMap.lookup(OutSec) + (SymAddr - SecAddr) / 0xffff;
assert(Index < PageEntriesNum);
return (HeaderEntriesNum + Index) * Config->Wordsize;
}
uint64_t MipsGotSection::getBodyEntryOffset(const SymbolBody &B,
int64_t Addend) const {
// Calculate offset of the GOT entries block: TLS, global, local.
uint64_t Index = HeaderEntriesNum + PageEntriesNum;
if (B.isTls())
Index += LocalEntries.size() + LocalEntries32.size() + GlobalEntries.size();
else if (B.IsInGlobalMipsGot)
Index += LocalEntries.size() + LocalEntries32.size();
else if (B.Is32BitMipsGot)
Index += LocalEntries.size();
// Calculate offset of the GOT entry in the block.
if (B.isInGot())
Index += B.GotIndex;
else {
auto It = EntryIndexMap.find({&B, Addend});
assert(It != EntryIndexMap.end());
Index += It->second;
}
return Index * Config->Wordsize;
}
uint64_t MipsGotSection::getTlsOffset() const {
return (getLocalEntriesNum() + GlobalEntries.size()) * Config->Wordsize;
}
uint64_t MipsGotSection::getGlobalDynOffset(const SymbolBody &B) const {
return B.GlobalDynIndex * Config->Wordsize;
}
const SymbolBody *MipsGotSection::getFirstGlobalEntry() const {
return GlobalEntries.empty() ? nullptr : GlobalEntries.front().first;
}
unsigned MipsGotSection::getLocalEntriesNum() const {
return HeaderEntriesNum + PageEntriesNum + LocalEntries.size() +
LocalEntries32.size();
}
void MipsGotSection::finalizeContents() { updateAllocSize(); }
void MipsGotSection::updateAllocSize() {
PageEntriesNum = 0;
for (std::pair<const OutputSection *, size_t> &P : PageIndexMap) {
// For each output section referenced by GOT page relocations calculate
// and save into PageIndexMap an upper bound of MIPS GOT entries required
// to store page addresses of local symbols. We assume the worst case -
// each 64kb page of the output section has at least one GOT relocation
// against it. And take in account the case when the section intersects
// page boundaries.
P.second = PageEntriesNum;
PageEntriesNum += getMipsPageCount(P.first->Size);
}
Size = (getLocalEntriesNum() + GlobalEntries.size() + TlsEntries.size()) *
Config->Wordsize;
}
bool MipsGotSection::empty() const {
// We add the .got section to the result for dynamic MIPS target because
// its address and properties are mentioned in the .dynamic section.
return Config->Relocatable;
}
uint64_t MipsGotSection::getGp() const { return ElfSym::MipsGp->getVA(0); }
static uint64_t readUint(uint8_t *Buf) {
if (Config->Is64)
return read64(Buf, Config->Endianness);
return read32(Buf, Config->Endianness);
}
static void writeUint(uint8_t *Buf, uint64_t Val) {
if (Config->Is64)
write64(Buf, Val, Config->Endianness);
else
write32(Buf, Val, Config->Endianness);
}
void MipsGotSection::writeTo(uint8_t *Buf) {
// Set the MSB of the second GOT slot. This is not required by any
// MIPS ABI documentation, though.
//
// There is a comment in glibc saying that "The MSB of got[1] of a
// gnu object is set to identify gnu objects," and in GNU gold it
// says "the second entry will be used by some runtime loaders".
// But how this field is being used is unclear.
//
// We are not really willing to mimic other linkers behaviors
// without understanding why they do that, but because all files
// generated by GNU tools have this special GOT value, and because
// we've been doing this for years, it is probably a safe bet to
// keep doing this for now. We really need to revisit this to see
// if we had to do this.
writeUint(Buf + Config->Wordsize, (uint64_t)1 << (Config->Wordsize * 8 - 1));
Buf += HeaderEntriesNum * Config->Wordsize;
// Write 'page address' entries to the local part of the GOT.
for (std::pair<const OutputSection *, size_t> &L : PageIndexMap) {
size_t PageCount = getMipsPageCount(L.first->Size);
uint64_t FirstPageAddr = getMipsPageAddr(L.first->Addr);
for (size_t PI = 0; PI < PageCount; ++PI) {
uint8_t *Entry = Buf + (L.second + PI) * Config->Wordsize;
writeUint(Entry, FirstPageAddr + PI * 0x10000);
}
}
Buf += PageEntriesNum * Config->Wordsize;
auto AddEntry = [&](const GotEntry &SA) {
uint8_t *Entry = Buf;
Buf += Config->Wordsize;
const SymbolBody *Body = SA.first;
uint64_t VA = Body->getVA(SA.second);
writeUint(Entry, VA);
};
std::for_each(std::begin(LocalEntries), std::end(LocalEntries), AddEntry);
std::for_each(std::begin(LocalEntries32), std::end(LocalEntries32), AddEntry);
std::for_each(std::begin(GlobalEntries), std::end(GlobalEntries), AddEntry);
// Initialize TLS-related GOT entries. If the entry has a corresponding
// dynamic relocations, leave it initialized by zero. Write down adjusted
// TLS symbol's values otherwise. To calculate the adjustments use offsets
// for thread-local storage.
// https://www.linux-mips.org/wiki/NPTL
if (TlsIndexOff != -1U && !Config->Pic)
writeUint(Buf + TlsIndexOff, 1);
for (const SymbolBody *B : TlsEntries) {
if (!B || B->isPreemptible())
continue;
uint64_t VA = B->getVA();
if (B->GotIndex != -1U) {
uint8_t *Entry = Buf + B->GotIndex * Config->Wordsize;
writeUint(Entry, VA - 0x7000);
}
if (B->GlobalDynIndex != -1U) {
uint8_t *Entry = Buf + B->GlobalDynIndex * Config->Wordsize;
writeUint(Entry, 1);
Entry += Config->Wordsize;
writeUint(Entry, VA - 0x8000);
}
}
}
GotPltSection::GotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotPltEntrySize, ".got.plt") {}
void GotPltSection::addEntry(SymbolBody &Sym) {
Sym.GotPltIndex = Target->GotPltHeaderEntriesNum + Entries.size();
Entries.push_back(&Sym);
}
size_t GotPltSection::getSize() const {
return (Target->GotPltHeaderEntriesNum + Entries.size()) *
Target->GotPltEntrySize;
}
void GotPltSection::writeTo(uint8_t *Buf) {
Target->writeGotPltHeader(Buf);
Buf += Target->GotPltHeaderEntriesNum * Target->GotPltEntrySize;
for (const SymbolBody *B : Entries) {
Target->writeGotPlt(Buf, *B);
Buf += Config->Wordsize;
}
}
// On ARM the IgotPltSection is part of the GotSection, on other Targets it is
// part of the .got.plt
IgotPltSection::IgotPltSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS,
Target->GotPltEntrySize,
Config->EMachine == EM_ARM ? ".got" : ".got.plt") {}
void IgotPltSection::addEntry(SymbolBody &Sym) {
Sym.IsInIgot = true;
Sym.GotPltIndex = Entries.size();
Entries.push_back(&Sym);
}
size_t IgotPltSection::getSize() const {
return Entries.size() * Target->GotPltEntrySize;
}
void IgotPltSection::writeTo(uint8_t *Buf) {
for (const SymbolBody *B : Entries) {
Target->writeIgotPlt(Buf, *B);
Buf += Config->Wordsize;
}
}
StringTableSection::StringTableSection(StringRef Name, bool Dynamic)
: SyntheticSection(Dynamic ? (uint64_t)SHF_ALLOC : 0, SHT_STRTAB, 1, Name),
Dynamic(Dynamic) {
// ELF string tables start with a NUL byte.
addString("");
}
// Adds a string to the string table. If HashIt is true we hash and check for
// duplicates. It is optional because the name of global symbols are already
// uniqued and hashing them again has a big cost for a small value: uniquing
// them with some other string that happens to be the same.
unsigned StringTableSection::addString(StringRef S, bool HashIt) {
if (HashIt) {
auto R = StringMap.insert(std::make_pair(S, this->Size));
if (!R.second)
return R.first->second;
}
unsigned Ret = this->Size;
this->Size = this->Size + S.size() + 1;
Strings.push_back(S);
return Ret;
}
void StringTableSection::writeTo(uint8_t *Buf) {
for (StringRef S : Strings) {
memcpy(Buf, S.data(), S.size());
Buf[S.size()] = '\0';
Buf += S.size() + 1;
}
}
// Returns the number of version definition entries. Because the first entry
// is for the version definition itself, it is the number of versioned symbols
// plus one. Note that we don't support multiple versions yet.
static unsigned getVerDefNum() { return Config->VersionDefinitions.size() + 1; }
template <class ELFT>
DynamicSection<ELFT>::DynamicSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_DYNAMIC, Config->Wordsize,
".dynamic") {
this->Entsize = ELFT::Is64Bits ? 16 : 8;
// .dynamic section is not writable on MIPS and on Fuchsia OS
// which passes -z rodynamic.
// See "Special Section" in Chapter 4 in the following document:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
if (Config->EMachine == EM_MIPS || Config->ZRodynamic)
this->Flags = SHF_ALLOC;
addEntries();
}
// There are some dynamic entries that don't depend on other sections.
// Such entries can be set early.
template <class ELFT> void DynamicSection<ELFT>::addEntries() {
// Add strings to .dynstr early so that .dynstr's size will be
// fixed early.
for (StringRef S : Config->FilterList)
add({DT_FILTER, InX::DynStrTab->addString(S)});
for (StringRef S : Config->AuxiliaryList)
add({DT_AUXILIARY, InX::DynStrTab->addString(S)});
if (!Config->Rpath.empty())
add({Config->EnableNewDtags ? DT_RUNPATH : DT_RPATH,
InX::DynStrTab->addString(Config->Rpath)});
for (SharedFile<ELFT> *F : SharedFile<ELFT>::Instances)
if (F->isNeeded())
add({DT_NEEDED, InX::DynStrTab->addString(F->SoName)});
if (!Config->SoName.empty())
add({DT_SONAME, InX::DynStrTab->addString(Config->SoName)});
// Set DT_FLAGS and DT_FLAGS_1.
uint32_t DtFlags = 0;
uint32_t DtFlags1 = 0;
if (Config->Bsymbolic)
DtFlags |= DF_SYMBOLIC;
if (Config->ZNodelete)
DtFlags1 |= DF_1_NODELETE;
if (Config->ZNodlopen)
DtFlags1 |= DF_1_NOOPEN;
if (Config->ZNow) {
DtFlags |= DF_BIND_NOW;
DtFlags1 |= DF_1_NOW;
}
if (Config->ZOrigin) {
DtFlags |= DF_ORIGIN;
DtFlags1 |= DF_1_ORIGIN;
}
if (DtFlags)
add({DT_FLAGS, DtFlags});
if (DtFlags1)
add({DT_FLAGS_1, DtFlags1});
// DT_DEBUG is a pointer to debug informaion used by debuggers at runtime. We
// need it for each process, so we don't write it for DSOs. The loader writes
// the pointer into this entry.
//
// DT_DEBUG is the only .dynamic entry that needs to be written to. Some
// systems (currently only Fuchsia OS) provide other means to give the
// debugger this information. Such systems may choose make .dynamic read-only.
// If the target is such a system (used -z rodynamic) don't write DT_DEBUG.
if (!Config->Shared && !Config->Relocatable && !Config->ZRodynamic)
add({DT_DEBUG, (uint64_t)0});
}
// Add remaining entries to complete .dynamic contents.
template <class ELFT> void DynamicSection<ELFT>::finalizeContents() {
if (this->Size)
return; // Already finalized.
this->Link = InX::DynStrTab->getParent()->SectionIndex;
if (In<ELFT>::RelaDyn->getParent() && !In<ELFT>::RelaDyn->empty()) {
bool IsRela = Config->IsRela;
add({IsRela ? DT_RELA : DT_REL, In<ELFT>::RelaDyn});
add({IsRela ? DT_RELASZ : DT_RELSZ, In<ELFT>::RelaDyn->getParent(),
Entry::SecSize});
add({IsRela ? DT_RELAENT : DT_RELENT,
uint64_t(IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel))});
// MIPS dynamic loader does not support RELCOUNT tag.
// The problem is in the tight relation between dynamic
// relocations and GOT. So do not emit this tag on MIPS.
if (Config->EMachine != EM_MIPS) {
size_t NumRelativeRels = In<ELFT>::RelaDyn->getRelativeRelocCount();
if (Config->ZCombreloc && NumRelativeRels)
add({IsRela ? DT_RELACOUNT : DT_RELCOUNT, NumRelativeRels});
}
}
if (In<ELFT>::RelaPlt->getParent() && !In<ELFT>::RelaPlt->empty()) {
add({DT_JMPREL, In<ELFT>::RelaPlt});
add({DT_PLTRELSZ, In<ELFT>::RelaPlt->getParent(), Entry::SecSize});
switch (Config->EMachine) {
case EM_MIPS:
add({DT_MIPS_PLTGOT, In<ELFT>::GotPlt});
break;
case EM_SPARCV9:
add({DT_PLTGOT, In<ELFT>::Plt});
break;
default:
add({DT_PLTGOT, In<ELFT>::GotPlt});
break;
}
add({DT_PLTREL, uint64_t(Config->IsRela ? DT_RELA : DT_REL)});
}
add({DT_SYMTAB, InX::DynSymTab});
add({DT_SYMENT, sizeof(Elf_Sym)});
add({DT_STRTAB, InX::DynStrTab});
add({DT_STRSZ, InX::DynStrTab->getSize()});
if (!Config->ZText)
add({DT_TEXTREL, (uint64_t)0});
if (InX::GnuHashTab)
add({DT_GNU_HASH, InX::GnuHashTab});
if (In<ELFT>::HashTab)
add({DT_HASH, In<ELFT>::HashTab});
if (Out::PreinitArray) {
add({DT_PREINIT_ARRAY, Out::PreinitArray});
add({DT_PREINIT_ARRAYSZ, Out::PreinitArray, Entry::SecSize});
}
if (Out::InitArray) {
add({DT_INIT_ARRAY, Out::InitArray});
add({DT_INIT_ARRAYSZ, Out::InitArray, Entry::SecSize});
}
if (Out::FiniArray) {
add({DT_FINI_ARRAY, Out::FiniArray});
add({DT_FINI_ARRAYSZ, Out::FiniArray, Entry::SecSize});
}
if (SymbolBody *B = Symtab->find(Config->Init))
if (B->isInCurrentDSO())
add({DT_INIT, B});
if (SymbolBody *B = Symtab->find(Config->Fini))
if (B->isInCurrentDSO())
add({DT_FINI, B});
bool HasVerNeed = In<ELFT>::VerNeed->getNeedNum() != 0;
if (HasVerNeed || In<ELFT>::VerDef)
add({DT_VERSYM, In<ELFT>::VerSym});
if (In<ELFT>::VerDef) {
add({DT_VERDEF, In<ELFT>::VerDef});
add({DT_VERDEFNUM, getVerDefNum()});
}
if (HasVerNeed) {
add({DT_VERNEED, In<ELFT>::VerNeed});
add({DT_VERNEEDNUM, In<ELFT>::VerNeed->getNeedNum()});
}
if (Config->EMachine == EM_MIPS) {
add({DT_MIPS_RLD_VERSION, 1});
add({DT_MIPS_FLAGS, RHF_NOTPOT});
add({DT_MIPS_BASE_ADDRESS, Config->ImageBase});
add({DT_MIPS_SYMTABNO, InX::DynSymTab->getNumSymbols()});
add({DT_MIPS_LOCAL_GOTNO, InX::MipsGot->getLocalEntriesNum()});
if (const SymbolBody *B = InX::MipsGot->getFirstGlobalEntry())
add({DT_MIPS_GOTSYM, B->DynsymIndex});
else
add({DT_MIPS_GOTSYM, InX::DynSymTab->getNumSymbols()});
add({DT_PLTGOT, InX::MipsGot});
if (InX::MipsRldMap)
add({DT_MIPS_RLD_MAP, InX::MipsRldMap});
}
getParent()->Link = this->Link;
// +1 for DT_NULL
this->Size = (Entries.size() + 1) * this->Entsize;
}
template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
for (const Entry &E : Entries) {
P->d_tag = E.Tag;
switch (E.Kind) {
case Entry::SecAddr:
P->d_un.d_ptr = E.OutSec->Addr;
break;
case Entry::InSecAddr:
P->d_un.d_ptr = E.InSec->getParent()->Addr + E.InSec->OutSecOff;
break;
case Entry::SecSize:
P->d_un.d_val = E.OutSec->Size;
break;
case Entry::SymAddr:
P->d_un.d_ptr = E.Sym->getVA();
break;
case Entry::PlainInt:
P->d_un.d_val = E.Val;
break;
}
++P;
}
}
uint64_t DynamicReloc::getOffset() const {
return InputSec->getOutputSection()->Addr + InputSec->getOffset(OffsetInSec);
}
int64_t DynamicReloc::getAddend() const {
if (UseSymVA)
return Sym->getVA(Addend);
return Addend;
}
uint32_t DynamicReloc::getSymIndex() const {
if (Sym && !UseSymVA)
return Sym->DynsymIndex;
return 0;
}
template <class ELFT>
RelocationSection<ELFT>::RelocationSection(StringRef Name, bool Sort)
: SyntheticSection(SHF_ALLOC, Config->IsRela ? SHT_RELA : SHT_REL,
Config->Wordsize, Name),
Sort(Sort) {
this->Entsize = Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
}
template <class ELFT>
void RelocationSection<ELFT>::addReloc(const DynamicReloc &Reloc) {
if (Reloc.Type == Target->RelativeRel)
++NumRelativeRelocs;
Relocs.push_back(Reloc);
}
template <class ELFT, class RelTy>
static bool compRelocations(const RelTy &A, const RelTy &B) {
bool AIsRel = A.getType(Config->IsMips64EL) == Target->RelativeRel;
bool BIsRel = B.getType(Config->IsMips64EL) == Target->RelativeRel;
if (AIsRel != BIsRel)
return AIsRel;
return A.getSymbol(Config->IsMips64EL) < B.getSymbol(Config->IsMips64EL);
}
template <class ELFT> void RelocationSection<ELFT>::writeTo(uint8_t *Buf) {
uint8_t *BufBegin = Buf;
for (const DynamicReloc &Rel : Relocs) {
auto *P = reinterpret_cast<Elf_Rela *>(Buf);
Buf += Config->IsRela ? sizeof(Elf_Rela) : sizeof(Elf_Rel);
if (Config->IsRela)
P->r_addend = Rel.getAddend();
P->r_offset = Rel.getOffset();
if (Config->EMachine == EM_MIPS && Rel.getInputSec() == InX::MipsGot)
// Dynamic relocation against MIPS GOT section make deal TLS entries
// allocated in the end of the GOT. We need to adjust the offset to take
// in account 'local' and 'global' GOT entries.
P->r_offset += InX::MipsGot->getTlsOffset();
P->setSymbolAndType(Rel.getSymIndex(), Rel.Type, Config->IsMips64EL);
}
if (Sort) {
if (Config->IsRela)
std::stable_sort((Elf_Rela *)BufBegin,
(Elf_Rela *)BufBegin + Relocs.size(),
compRelocations<ELFT, Elf_Rela>);
else
std::stable_sort((Elf_Rel *)BufBegin, (Elf_Rel *)BufBegin + Relocs.size(),
compRelocations<ELFT, Elf_Rel>);
}
}
template <class ELFT> unsigned RelocationSection<ELFT>::getRelocOffset() {
return this->Entsize * Relocs.size();
}
template <class ELFT> void RelocationSection<ELFT>::finalizeContents() {
this->Link = InX::DynSymTab ? InX::DynSymTab->getParent()->SectionIndex
: InX::SymTab->getParent()->SectionIndex;
// Set required output section properties.
getParent()->Link = this->Link;
}
SymbolTableBaseSection::SymbolTableBaseSection(StringTableSection &StrTabSec)
: SyntheticSection(StrTabSec.isDynamic() ? (uint64_t)SHF_ALLOC : 0,
StrTabSec.isDynamic() ? SHT_DYNSYM : SHT_SYMTAB,
Config->Wordsize,
StrTabSec.isDynamic() ? ".dynsym" : ".symtab"),
StrTabSec(StrTabSec) {}
// Orders symbols according to their positions in the GOT,
// in compliance with MIPS ABI rules.
// See "Global Offset Table" in Chapter 5 in the following document
// for detailed description:
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
static bool sortMipsSymbols(const SymbolTableEntry &L,
const SymbolTableEntry &R) {
// Sort entries related to non-local preemptible symbols by GOT indexes.
// All other entries go to the first part of GOT in arbitrary order.
bool LIsInLocalGot = !L.Symbol->IsInGlobalMipsGot;
bool RIsInLocalGot = !R.Symbol->IsInGlobalMipsGot;
if (LIsInLocalGot || RIsInLocalGot)
return !RIsInLocalGot;
return L.Symbol->GotIndex < R.Symbol->GotIndex;
}
// Finalize a symbol table. The ELF spec requires that all local
// symbols precede global symbols, so we sort symbol entries in this
// function. (For .dynsym, we don't do that because symbols for
// dynamic linking are inherently all globals.)
void SymbolTableBaseSection::finalizeContents() {
getParent()->Link = StrTabSec.getParent()->SectionIndex;
// If it is a .dynsym, there should be no local symbols, but we need
// to do a few things for the dynamic linker.
if (this->Type == SHT_DYNSYM) {
// Section's Info field has the index of the first non-local symbol.
// Because the first symbol entry is a null entry, 1 is the first.
getParent()->Info = 1;
if (InX::GnuHashTab) {
// NB: It also sorts Symbols to meet the GNU hash table requirements.
InX::GnuHashTab->addSymbols(Symbols);
} else if (Config->EMachine == EM_MIPS) {
std::stable_sort(Symbols.begin(), Symbols.end(), sortMipsSymbols);
}
size_t I = 0;
for (const SymbolTableEntry &S : Symbols)
S.Symbol->DynsymIndex = ++I;
return;
}
}
void SymbolTableBaseSection::postThunkContents() {
if (this->Type == SHT_DYNSYM)
return;
// move all local symbols before global symbols.
auto It = std::stable_partition(
Symbols.begin(), Symbols.end(), [](const SymbolTableEntry &S) {
return S.Symbol->isLocal() ||
S.Symbol->symbol()->computeBinding() == STB_LOCAL;
});
size_t NumLocals = It - Symbols.begin();
getParent()->Info = NumLocals + 1;
}
void SymbolTableBaseSection::addSymbol(SymbolBody *B) {
// Adding a local symbol to a .dynsym is a bug.
assert(this->Type != SHT_DYNSYM || !B->isLocal());
bool HashIt = B->isLocal();
Symbols.push_back({B, StrTabSec.addString(B->getName(), HashIt)});
}
size_t SymbolTableBaseSection::getSymbolIndex(SymbolBody *Body) {
auto I = llvm::find_if(Symbols, [&](const SymbolTableEntry &E) {
if (E.Symbol == Body)
return true;
// This is used for -r, so we have to handle multiple section
// symbols being combined.
if (Body->Type == STT_SECTION && E.Symbol->Type == STT_SECTION)
return Body->getOutputSection() == E.Symbol->getOutputSection();
return false;
});
if (I == Symbols.end())
return 0;
return I - Symbols.begin() + 1;
}
template <class ELFT>
SymbolTableSection<ELFT>::SymbolTableSection(StringTableSection &StrTabSec)
: SymbolTableBaseSection(StrTabSec) {
this->Entsize = sizeof(Elf_Sym);
}
// Write the internal symbol table contents to the output symbol table.
template <class ELFT> void SymbolTableSection<ELFT>::writeTo(uint8_t *Buf) {
// The first entry is a null entry as per the ELF spec.
Buf += sizeof(Elf_Sym);
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
for (SymbolTableEntry &Ent : Symbols) {
SymbolBody *Body = Ent.Symbol;
// Set st_info and st_other.
if (Body->isLocal()) {
ESym->setBindingAndType(STB_LOCAL, Body->Type);
} else {
ESym->setBindingAndType(Body->symbol()->computeBinding(), Body->Type);
ESym->setVisibility(Body->symbol()->Visibility);
}
ESym->st_name = Ent.StrTabOffset;
// Set a section index.
if (const OutputSection *OutSec = Body->getOutputSection())
ESym->st_shndx = OutSec->SectionIndex;
else if (isa<DefinedRegular>(Body))
ESym->st_shndx = SHN_ABS;
else if (isa<DefinedCommon>(Body))
ESym->st_shndx = SHN_COMMON;
// Copy symbol size if it is a defined symbol. st_size is not significant
// for undefined symbols, so whether copying it or not is up to us if that's
// the case. We'll leave it as zero because by not setting a value, we can
// get the exact same outputs for two sets of input files that differ only
// in undefined symbol size in DSOs.
if (ESym->st_shndx != SHN_UNDEF)
ESym->st_size = Body->getSize<ELFT>();
// st_value is usually an address of a symbol, but that has a
// special meaining for uninstantiated common symbols (this can
// occur if -r is given).
if (!Config->DefineCommon && isa<DefinedCommon>(Body))
ESym->st_value = cast<DefinedCommon>(Body)->Alignment;
else
ESym->st_value = Body->getVA();
++ESym;
}
// On MIPS we need to mark symbol which has a PLT entry and requires
// pointer equality by STO_MIPS_PLT flag. That is necessary to help
// dynamic linker distinguish such symbols and MIPS lazy-binding stubs.
// https://sourceware.org/ml/binutils/2008-07/txt00000.txt
if (Config->EMachine == EM_MIPS) {
auto *ESym = reinterpret_cast<Elf_Sym *>(Buf);
for (SymbolTableEntry &Ent : Symbols) {
SymbolBody *Body = Ent.Symbol;
if (Body->isInPlt() && Body->NeedsPltAddr)
ESym->st_other |= STO_MIPS_PLT;
if (Config->Relocatable)
if (auto *D = dyn_cast<DefinedRegular>(Body))
if (D->isMipsPIC<ELFT>())
ESym->st_other |= STO_MIPS_PIC;
++ESym;
}
}
}
// .hash and .gnu.hash sections contain on-disk hash tables that map
// symbol names to their dynamic symbol table indices. Their purpose
// is to help the dynamic linker resolve symbols quickly. If ELF files
// don't have them, the dynamic linker has to do linear search on all
// dynamic symbols, which makes programs slower. Therefore, a .hash
// section is added to a DSO by default. A .gnu.hash is added if you
// give the -hash-style=gnu or -hash-style=both option.
//
// The Unix semantics of resolving dynamic symbols is somewhat expensive.
// Each ELF file has a list of DSOs that the ELF file depends on and a
// list of dynamic symbols that need to be resolved from any of the
// DSOs. That means resolving all dynamic symbols takes O(m)*O(n)
// where m is the number of DSOs and n is the number of dynamic
// symbols. For modern large programs, both m and n are large. So
// making each step faster by using hash tables substiantially
// improves time to load programs.
//
// (Note that this is not the only way to design the shared library.
// For instance, the Windows DLL takes a different approach. On
// Windows, each dynamic symbol has a name of DLL from which the symbol
// has to be resolved. That makes the cost of symbol resolution O(n).
// This disables some hacky techniques you can use on Unix such as
// LD_PRELOAD, but this is arguably better semantics than the Unix ones.)
//
// Due to historical reasons, we have two different hash tables, .hash
// and .gnu.hash. They are for the same purpose, and .gnu.hash is a new
// and better version of .hash. .hash is just an on-disk hash table, but
// .gnu.hash has a bloom filter in addition to a hash table to skip
// DSOs very quickly. If you are sure that your dynamic linker knows
// about .gnu.hash, you want to specify -hash-style=gnu. Otherwise, a
// safe bet is to specify -hash-style=both for backward compatibilty.
GnuHashTableSection::GnuHashTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_HASH, Config->Wordsize, ".gnu.hash") {
}
void GnuHashTableSection::finalizeContents() {
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
// Computes bloom filter size in word size. We want to allocate 8
// bits for each symbol. It must be a power of two.
if (Symbols.empty())
MaskWords = 1;
else
MaskWords = NextPowerOf2((Symbols.size() - 1) / Config->Wordsize);
Size = 16; // Header
Size += Config->Wordsize * MaskWords; // Bloom filter
Size += NBuckets * 4; // Hash buckets
Size += Symbols.size() * 4; // Hash values
}
void GnuHashTableSection::writeTo(uint8_t *Buf) {
// Write a header.
write32(Buf, NBuckets, Config->Endianness);
write32(Buf + 4, InX::DynSymTab->getNumSymbols() - Symbols.size(),
Config->Endianness);
write32(Buf + 8, MaskWords, Config->Endianness);
write32(Buf + 12, getShift2(), Config->Endianness);
Buf += 16;
// Write a bloom filter and a hash table.
writeBloomFilter(Buf);
Buf += Config->Wordsize * MaskWords;
writeHashTable(Buf);
}
// This function writes a 2-bit bloom filter. This bloom filter alone
// usually filters out 80% or more of all symbol lookups [1].
// The dynamic linker uses the hash table only when a symbol is not
// filtered out by a bloom filter.
//
// [1] Ulrich Drepper (2011), "How To Write Shared Libraries" (Ver. 4.1.2),
// p.9, https://www.akkadia.org/drepper/dsohowto.pdf
void GnuHashTableSection::writeBloomFilter(uint8_t *Buf) {
const unsigned C = Config->Wordsize * 8;
for (const Entry &Sym : Symbols) {
size_t I = (Sym.Hash / C) & (MaskWords - 1);
uint64_t Val = readUint(Buf + I * Config->Wordsize);
Val |= uint64_t(1) << (Sym.Hash % C);
Val |= uint64_t(1) << ((Sym.Hash >> getShift2()) % C);
writeUint(Buf + I * Config->Wordsize, Val);
}
}
void GnuHashTableSection::writeHashTable(uint8_t *Buf) {
// Group symbols by hash value.
std::vector<std::vector<Entry>> Syms(NBuckets);
for (const Entry &Ent : Symbols)
Syms[Ent.Hash % NBuckets].push_back(Ent);
// Write hash buckets. Hash buckets contain indices in the following
// hash value table.
uint32_t *Buckets = reinterpret_cast<uint32_t *>(Buf);
for (size_t I = 0; I < NBuckets; ++I)
if (!Syms[I].empty())
write32(Buckets + I, Syms[I][0].Body->DynsymIndex, Config->Endianness);
// Write a hash value table. It represents a sequence of chains that
// share the same hash modulo value. The last element of each chain
// is terminated by LSB 1.
uint32_t *Values = Buckets + NBuckets;
size_t I = 0;
for (std::vector<Entry> &Vec : Syms) {
if (Vec.empty())
continue;
for (const Entry &Ent : makeArrayRef(Vec).drop_back())
write32(Values + I++, Ent.Hash & ~1, Config->Endianness);
write32(Values + I++, Vec.back().Hash | 1, Config->Endianness);
}
}
static uint32_t hashGnu(StringRef Name) {
uint32_t H = 5381;
for (uint8_t C : Name)
H = (H << 5) + H + C;
return H;
}
// Returns a number of hash buckets to accomodate given number of elements.
// We want to choose a moderate number that is not too small (which
// causes too many hash collisions) and not too large (which wastes
// disk space.)
//
// We return a prime number because it (is believed to) achieve good
// hash distribution.
static size_t getBucketSize(size_t NumSymbols) {
// List of largest prime numbers that are not greater than 2^n + 1.
for (size_t N : {131071, 65521, 32749, 16381, 8191, 4093, 2039, 1021, 509,
251, 127, 61, 31, 13, 7, 3, 1})
if (N <= NumSymbols)
return N;
return 0;
}
// Add symbols to this symbol hash table. Note that this function
// destructively sort a given vector -- which is needed because
// GNU-style hash table places some sorting requirements.
void GnuHashTableSection::addSymbols(std::vector<SymbolTableEntry> &V) {
// We cannot use 'auto' for Mid because GCC 6.1 cannot deduce
// its type correctly.
std::vector<SymbolTableEntry>::iterator Mid =
std::stable_partition(V.begin(), V.end(), [](const SymbolTableEntry &S) {
return S.Symbol->isUndefined();
});
if (Mid == V.end())
return;
for (SymbolTableEntry &Ent : llvm::make_range(Mid, V.end())) {
SymbolBody *B = Ent.Symbol;
Symbols.push_back({B, Ent.StrTabOffset, hashGnu(B->getName())});
}
NBuckets = getBucketSize(Symbols.size());
std::stable_sort(Symbols.begin(), Symbols.end(),
[&](const Entry &L, const Entry &R) {
return L.Hash % NBuckets < R.Hash % NBuckets;
});
V.erase(Mid, V.end());
for (const Entry &Ent : Symbols)
V.push_back({Ent.Body, Ent.StrTabOffset});
}
template <class ELFT>
HashTableSection<ELFT>::HashTableSection()
: SyntheticSection(SHF_ALLOC, SHT_HASH, 4, ".hash") {
this->Entsize = 4;
}
template <class ELFT> void HashTableSection<ELFT>::finalizeContents() {
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
unsigned NumEntries = 2; // nbucket and nchain.
NumEntries += InX::DynSymTab->getNumSymbols(); // The chain entries.
// Create as many buckets as there are symbols.
// FIXME: This is simplistic. We can try to optimize it, but implementing
// support for SHT_GNU_HASH is probably even more profitable.
NumEntries += InX::DynSymTab->getNumSymbols();
this->Size = NumEntries * 4;
}
template <class ELFT> void HashTableSection<ELFT>::writeTo(uint8_t *Buf) {
// A 32-bit integer type in the target endianness.
typedef typename ELFT::Word Elf_Word;
unsigned NumSymbols = InX::DynSymTab->getNumSymbols();
auto *P = reinterpret_cast<Elf_Word *>(Buf);
*P++ = NumSymbols; // nbucket
*P++ = NumSymbols; // nchain
Elf_Word *Buckets = P;
Elf_Word *Chains = P + NumSymbols;
for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
SymbolBody *Body = S.Symbol;
StringRef Name = Body->getName();
unsigned I = Body->DynsymIndex;
uint32_t Hash = hashSysV(Name) % NumSymbols;
Chains[I] = Buckets[Hash];
Buckets[Hash] = I;
}
}
PltSection::PltSection(size_t S)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS, 16, ".plt"),
HeaderSize(S) {
// The PLT needs to be writable on SPARC as the dynamic linker will
// modify the instructions in the PLT entries.
if (Config->EMachine == EM_SPARCV9)
this->Flags |= SHF_WRITE;
}
void PltSection::writeTo(uint8_t *Buf) {
// At beginning of PLT but not the IPLT, we have code to call the dynamic
// linker to resolve dynsyms at runtime. Write such code.
if (HeaderSize != 0)
Target->writePltHeader(Buf);
size_t Off = HeaderSize;
// The IPlt is immediately after the Plt, account for this in RelOff
unsigned PltOff = getPltRelocOff();
for (auto &I : Entries) {
const SymbolBody *B = I.first;
unsigned RelOff = I.second + PltOff;
uint64_t Got = B->getGotPltVA();
uint64_t Plt = this->getVA() + Off;
Target->writePlt(Buf + Off, Got, Plt, B->PltIndex, RelOff);
Off += Target->PltEntrySize;
}
}
template <class ELFT> void PltSection::addEntry(SymbolBody &Sym) {
Sym.PltIndex = Entries.size();
RelocationSection<ELFT> *PltRelocSection = In<ELFT>::RelaPlt;
if (HeaderSize == 0) {
PltRelocSection = In<ELFT>::RelaIplt;
Sym.IsInIplt = true;
}
unsigned RelOff = PltRelocSection->getRelocOffset();
Entries.push_back(std::make_pair(&Sym, RelOff));
}
size_t PltSection::getSize() const {
return HeaderSize + Entries.size() * Target->PltEntrySize;
}
// Some architectures such as additional symbols in the PLT section. For
// example ARM uses mapping symbols to aid disassembly
void PltSection::addSymbols() {
// The PLT may have symbols defined for the Header, the IPLT has no header
if (HeaderSize != 0)
Target->addPltHeaderSymbols(this);
size_t Off = HeaderSize;
for (size_t I = 0; I < Entries.size(); ++I) {
Target->addPltSymbols(this, Off);
Off += Target->PltEntrySize;
}
}
unsigned PltSection::getPltRelocOff() const {
return (HeaderSize == 0) ? InX::Plt->getSize() : 0;
}
GdbIndexSection::GdbIndexSection(std::vector<GdbIndexChunk> &&Chunks)
: SyntheticSection(0, SHT_PROGBITS, 1, ".gdb_index"),
StringPool(llvm::StringTableBuilder::ELF), Chunks(std::move(Chunks)) {}
// The hash function used for .gdb_index version 5 or above.
static uint32_t gdbHash(StringRef Str) {
uint32_t R = 0;
for (uint8_t C : Str)
R = R * 67 + tolower(C) - 113;
return R;
}
static std::vector<CompilationUnitEntry> readCuList(DWARFContext &Dwarf) {
std::vector<CompilationUnitEntry> Ret;
for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units())
Ret.push_back({CU->getOffset(), CU->getLength() + 4});
return Ret;
}
static std::vector<AddressEntry> readAddressArea(DWARFContext &Dwarf,
InputSection *Sec) {
std::vector<AddressEntry> Ret;
uint32_t CurrentCu = 0;
for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf.compile_units()) {
DWARFAddressRangesVector Ranges;
CU->collectAddressRanges(Ranges);
ArrayRef<InputSectionBase *> Sections = Sec->File->getSections();
for (DWARFAddressRange &R : Ranges) {
InputSectionBase *S = Sections[R.SectionIndex];
if (!S || S == &InputSection::Discarded || !S->Live)
continue;
// Range list with zero size has no effect.
if (R.LowPC == R.HighPC)
continue;
auto *IS = cast<InputSection>(S);
uint64_t Offset = IS->getOffsetInFile();
Ret.push_back({IS, R.LowPC - Offset, R.HighPC - Offset, CurrentCu});
}
++CurrentCu;
}
return Ret;
}
static std::vector<NameTypeEntry> readPubNamesAndTypes(DWARFContext &Dwarf,
bool IsLE) {
StringRef Data[] = {Dwarf.getDWARFObj().getGnuPubNamesSection(),
Dwarf.getDWARFObj().getGnuPubTypesSection()};
std::vector<NameTypeEntry> Ret;
for (StringRef D : Data) {
DWARFDebugPubTable PubTable(D, IsLE, true);
for (const DWARFDebugPubTable::Set &Set : PubTable.getData())
for (const DWARFDebugPubTable::Entry &Ent : Set.Entries)
Ret.push_back({Ent.Name, Ent.Descriptor.toBits()});
}
return Ret;
}
static std::vector<InputSection *> getDebugInfoSections() {
std::vector<InputSection *> Ret;
for (InputSectionBase *S : InputSections)
if (InputSection *IS = dyn_cast<InputSection>(S))
if (IS->Name == ".debug_info")
Ret.push_back(IS);
return Ret;
}
void GdbIndexSection::buildIndex() {
if (Chunks.empty())
return;
uint32_t CuId = 0;
for (GdbIndexChunk &D : Chunks) {
for (AddressEntry &E : D.AddressArea)
E.CuIndex += CuId;
// Populate constant pool area.
for (NameTypeEntry &NameType : D.NamesAndTypes) {
uint32_t Hash = gdbHash(NameType.Name);
size_t Offset = StringPool.add(NameType.Name);
bool IsNew;
GdbSymbol *Sym;
std::tie(IsNew, Sym) = SymbolTable.add(Hash, Offset);
if (IsNew) {
Sym->CuVectorIndex = CuVectors.size();
CuVectors.resize(CuVectors.size() + 1);
}
CuVectors[Sym->CuVectorIndex].insert(CuId | (NameType.Type << 24));
}
CuId += D.CompilationUnits.size();
}
}
static GdbIndexChunk readDwarf(DWARFContext &Dwarf, InputSection *Sec) {
GdbIndexChunk Ret;
Ret.DebugInfoSec = Sec;
Ret.CompilationUnits = readCuList(Dwarf);
Ret.AddressArea = readAddressArea(Dwarf, Sec);
Ret.NamesAndTypes = readPubNamesAndTypes(Dwarf, Config->IsLE);
return Ret;
}
template <class ELFT> GdbIndexSection *elf::createGdbIndex() {
std::vector<InputSection *> Sections = getDebugInfoSections();
std::vector<GdbIndexChunk> Chunks(Sections.size());
parallelForEachN(0, Chunks.size(), [&](size_t I) {
ObjFile<ELFT> *F = Sections[I]->getFile<ELFT>();
DWARFContext Dwarf(make_unique<LLDDwarfObj<ELFT>>(F));
Chunks[I] = readDwarf(Dwarf, Sections[I]);
});
return make<GdbIndexSection>(std::move(Chunks));
}
static size_t getCuSize(ArrayRef<GdbIndexChunk> Arr) {
size_t Ret = 0;
for (const GdbIndexChunk &D : Arr)
Ret += D.CompilationUnits.size();
return Ret;
}
static size_t getAddressAreaSize(ArrayRef<GdbIndexChunk> Arr) {
size_t Ret = 0;
for (const GdbIndexChunk &D : Arr)
Ret += D.AddressArea.size();
return Ret;
}
void GdbIndexSection::finalizeContents() {
if (Finalized)
return;
Finalized = true;
buildIndex();
SymbolTable.finalizeContents();
// GdbIndex header consist from version fields
// and 5 more fields with different kinds of offsets.
CuTypesOffset = CuListOffset + getCuSize(Chunks) * CompilationUnitSize;
SymTabOffset = CuTypesOffset + getAddressAreaSize(Chunks) * AddressEntrySize;
ConstantPoolOffset =
SymTabOffset + SymbolTable.getCapacity() * SymTabEntrySize;
for (std::set<uint32_t> &CuVec : CuVectors) {
CuVectorsOffset.push_back(CuVectorsSize);
CuVectorsSize += OffsetTypeSize * (CuVec.size() + 1);
}
StringPoolOffset = ConstantPoolOffset + CuVectorsSize;
StringPool.finalizeInOrder();
}
size_t GdbIndexSection::getSize() const {
const_cast<GdbIndexSection *>(this)->finalizeContents();
return StringPoolOffset + StringPool.getSize();
}
void GdbIndexSection::writeTo(uint8_t *Buf) {
write32le(Buf, 7); // Write version.
write32le(Buf + 4, CuListOffset); // CU list offset.
write32le(Buf + 8, CuTypesOffset); // Types CU list offset.
write32le(Buf + 12, CuTypesOffset); // Address area offset.
write32le(Buf + 16, SymTabOffset); // Symbol table offset.
write32le(Buf + 20, ConstantPoolOffset); // Constant pool offset.
Buf += 24;
// Write the CU list.
for (GdbIndexChunk &D : Chunks) {
for (CompilationUnitEntry &Cu : D.CompilationUnits) {
write64le(Buf, D.DebugInfoSec->OutSecOff + Cu.CuOffset);
write64le(Buf + 8, Cu.CuLength);
Buf += 16;
}
}
// Write the address area.
for (GdbIndexChunk &D : Chunks) {
for (AddressEntry &E : D.AddressArea) {
uint64_t BaseAddr =
E.Section->getParent()->Addr + E.Section->getOffset(0);
write64le(Buf, BaseAddr + E.LowAddress);
write64le(Buf + 8, BaseAddr + E.HighAddress);
write32le(Buf + 16, E.CuIndex);
Buf += 20;
}
}
// Write the symbol table.
for (size_t I = 0; I < SymbolTable.getCapacity(); ++I) {
GdbSymbol *Sym = SymbolTable.getSymbol(I);
if (Sym) {
size_t NameOffset =
Sym->NameOffset + StringPoolOffset - ConstantPoolOffset;
size_t CuVectorOffset = CuVectorsOffset[Sym->CuVectorIndex];
write32le(Buf, NameOffset);
write32le(Buf + 4, CuVectorOffset);
}
Buf += 8;
}
// Write the CU vectors into the constant pool.
for (std::set<uint32_t> &CuVec : CuVectors) {
write32le(Buf, CuVec.size());
Buf += 4;
for (uint32_t Val : CuVec) {
write32le(Buf, Val);
Buf += 4;
}
}
StringPool.write(Buf);
}
bool GdbIndexSection::empty() const { return !Out::DebugInfo; }
template <class ELFT>
EhFrameHeader<ELFT>::EhFrameHeader()
: SyntheticSection(SHF_ALLOC, SHT_PROGBITS, 1, ".eh_frame_hdr") {}
// .eh_frame_hdr contains a binary search table of pointers to FDEs.
// Each entry of the search table consists of two values,
// the starting PC from where FDEs covers, and the FDE's address.
// It is sorted by PC.
template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
const endianness E = ELFT::TargetEndianness;
// Sort the FDE list by their PC and uniqueify. Usually there is only
// one FDE for a PC (i.e. function), but if ICF merges two functions
// into one, there can be more than one FDEs pointing to the address.
auto Less = [](const FdeData &A, const FdeData &B) { return A.Pc < B.Pc; };
std::stable_sort(Fdes.begin(), Fdes.end(), Less);
auto Eq = [](const FdeData &A, const FdeData &B) { return A.Pc == B.Pc; };
Fdes.erase(std::unique(Fdes.begin(), Fdes.end(), Eq), Fdes.end());
Buf[0] = 1;
Buf[1] = DW_EH_PE_pcrel | DW_EH_PE_sdata4;
Buf[2] = DW_EH_PE_udata4;
Buf[3] = DW_EH_PE_datarel | DW_EH_PE_sdata4;
write32<E>(Buf + 4, In<ELFT>::EhFrame->getParent()->Addr - this->getVA() - 4);
write32<E>(Buf + 8, Fdes.size());
Buf += 12;
uint64_t VA = this->getVA();
for (FdeData &Fde : Fdes) {
write32<E>(Buf, Fde.Pc - VA);
write32<E>(Buf + 4, Fde.FdeVA - VA);
Buf += 8;
}
}
template <class ELFT> size_t EhFrameHeader<ELFT>::getSize() const {
// .eh_frame_hdr has a 12 bytes header followed by an array of FDEs.
return 12 + In<ELFT>::EhFrame->NumFdes * 8;
}
template <class ELFT>
void EhFrameHeader<ELFT>::addFde(uint32_t Pc, uint32_t FdeVA) {
Fdes.push_back({Pc, FdeVA});
}
template <class ELFT> bool EhFrameHeader<ELFT>::empty() const {
return In<ELFT>::EhFrame->empty();
}
template <class ELFT>
VersionDefinitionSection<ELFT>::VersionDefinitionSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verdef, sizeof(uint32_t),
".gnu.version_d") {}
static StringRef getFileDefName() {
if (!Config->SoName.empty())
return Config->SoName;
return Config->OutputFile;
}
template <class ELFT> void VersionDefinitionSection<ELFT>::finalizeContents() {
FileDefNameOff = InX::DynStrTab->addString(getFileDefName());
for (VersionDefinition &V : Config->VersionDefinitions)
V.NameOff = InX::DynStrTab->addString(V.Name);
getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
// sh_info should be set to the number of definitions. This fact is missed in
// documentation, but confirmed by binutils community:
// https://sourceware.org/ml/binutils/2014-11/msg00355.html
getParent()->Info = getVerDefNum();
}
template <class ELFT>
void VersionDefinitionSection<ELFT>::writeOne(uint8_t *Buf, uint32_t Index,
StringRef Name, size_t NameOff) {
auto *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
Verdef->vd_version = 1;
Verdef->vd_cnt = 1;
Verdef->vd_aux = sizeof(Elf_Verdef);
Verdef->vd_next = sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
Verdef->vd_flags = (Index == 1 ? VER_FLG_BASE : 0);
Verdef->vd_ndx = Index;
Verdef->vd_hash = hashSysV(Name);
auto *Verdaux = reinterpret_cast<Elf_Verdaux *>(Buf + sizeof(Elf_Verdef));
Verdaux->vda_name = NameOff;
Verdaux->vda_next = 0;
}
template <class ELFT>
void VersionDefinitionSection<ELFT>::writeTo(uint8_t *Buf) {
writeOne(Buf, 1, getFileDefName(), FileDefNameOff);
for (VersionDefinition &V : Config->VersionDefinitions) {
Buf += sizeof(Elf_Verdef) + sizeof(Elf_Verdaux);
writeOne(Buf, V.Id, V.Name, V.NameOff);
}
// Need to terminate the last version definition.
Elf_Verdef *Verdef = reinterpret_cast<Elf_Verdef *>(Buf);
Verdef->vd_next = 0;
}
template <class ELFT> size_t VersionDefinitionSection<ELFT>::getSize() const {
return (sizeof(Elf_Verdef) + sizeof(Elf_Verdaux)) * getVerDefNum();
}
template <class ELFT>
VersionTableSection<ELFT>::VersionTableSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_versym, sizeof(uint16_t),
".gnu.version") {
this->Entsize = sizeof(Elf_Versym);
}
template <class ELFT> void VersionTableSection<ELFT>::finalizeContents() {
// At the moment of june 2016 GNU docs does not mention that sh_link field
// should be set, but Sun docs do. Also readelf relies on this field.
getParent()->Link = InX::DynSymTab->getParent()->SectionIndex;
}
template <class ELFT> size_t VersionTableSection<ELFT>::getSize() const {
return sizeof(Elf_Versym) * (InX::DynSymTab->getSymbols().size() + 1);
}
template <class ELFT> void VersionTableSection<ELFT>::writeTo(uint8_t *Buf) {
auto *OutVersym = reinterpret_cast<Elf_Versym *>(Buf) + 1;
for (const SymbolTableEntry &S : InX::DynSymTab->getSymbols()) {
OutVersym->vs_index = S.Symbol->symbol()->VersionId;
++OutVersym;
}
}
template <class ELFT> bool VersionTableSection<ELFT>::empty() const {
return !In<ELFT>::VerDef && In<ELFT>::VerNeed->empty();
}
template <class ELFT>
VersionNeedSection<ELFT>::VersionNeedSection()
: SyntheticSection(SHF_ALLOC, SHT_GNU_verneed, sizeof(uint32_t),
".gnu.version_r") {
// Identifiers in verneed section start at 2 because 0 and 1 are reserved
// for VER_NDX_LOCAL and VER_NDX_GLOBAL.
// First identifiers are reserved by verdef section if it exist.
NextIndex = getVerDefNum() + 1;
}
template <class ELFT>
void VersionNeedSection<ELFT>::addSymbol(SharedSymbol *SS) {
auto *Ver = reinterpret_cast<const typename ELFT::Verdef *>(SS->Verdef);
if (!Ver) {
SS->symbol()->VersionId = VER_NDX_GLOBAL;
return;
}
SharedFile<ELFT> *File = SS->getFile<ELFT>();
// If we don't already know that we need an Elf_Verneed for this DSO, prepare
// to create one by adding it to our needed list and creating a dynstr entry
// for the soname.
if (File->VerdefMap.empty())
Needed.push_back({File, InX::DynStrTab->addString(File->SoName)});
typename SharedFile<ELFT>::NeededVer &NV = File->VerdefMap[Ver];
// If we don't already know that we need an Elf_Vernaux for this Elf_Verdef,
// prepare to create one by allocating a version identifier and creating a
// dynstr entry for the version name.
if (NV.Index == 0) {
NV.StrTab = InX::DynStrTab->addString(File->getStringTable().data() +
Ver->getAux()->vda_name);
NV.Index = NextIndex++;
}
SS->symbol()->VersionId = NV.Index;
}
template <class ELFT> void VersionNeedSection<ELFT>::writeTo(uint8_t *Buf) {
// The Elf_Verneeds need to appear first, followed by the Elf_Vernauxs.
auto *Verneed = reinterpret_cast<Elf_Verneed *>(Buf);
auto *Vernaux = reinterpret_cast<Elf_Vernaux *>(Verneed + Needed.size());
for (std::pair<SharedFile<ELFT> *, size_t> &P : Needed) {
// Create an Elf_Verneed for this DSO.
Verneed->vn_version = 1;
Verneed->vn_cnt = P.first->VerdefMap.size();
Verneed->vn_file = P.second;
Verneed->vn_aux =
reinterpret_cast<char *>(Vernaux) - reinterpret_cast<char *>(Verneed);
Verneed->vn_next = sizeof(Elf_Verneed);
++Verneed;
// Create the Elf_Vernauxs for this Elf_Verneed. The loop iterates over
// VerdefMap, which will only contain references to needed version
// definitions. Each Elf_Vernaux is based on the information contained in
// the Elf_Verdef in the source DSO. This loop iterates over a std::map of
// pointers, but is deterministic because the pointers refer to Elf_Verdef
// data structures within a single input file.
for (auto &NV : P.first->VerdefMap) {
Vernaux->vna_hash = NV.first->vd_hash;
Vernaux->vna_flags = 0;
Vernaux->vna_other = NV.second.Index;
Vernaux->vna_name = NV.second.StrTab;
Vernaux->vna_next = sizeof(Elf_Vernaux);
++Vernaux;
}
Vernaux[-1].vna_next = 0;
}
Verneed[-1].vn_next = 0;
}
template <class ELFT> void VersionNeedSection<ELFT>::finalizeContents() {
getParent()->Link = InX::DynStrTab->getParent()->SectionIndex;
getParent()->Info = Needed.size();
}
template <class ELFT> size_t VersionNeedSection<ELFT>::getSize() const {
unsigned Size = Needed.size() * sizeof(Elf_Verneed);
for (const std::pair<SharedFile<ELFT> *, size_t> &P : Needed)
Size += P.first->VerdefMap.size() * sizeof(Elf_Vernaux);
return Size;
}
template <class ELFT> bool VersionNeedSection<ELFT>::empty() const {
return getNeedNum() == 0;
}
MergeSyntheticSection::MergeSyntheticSection(StringRef Name, uint32_t Type,
uint64_t Flags, uint32_t Alignment)
: SyntheticSection(Flags, Type, Alignment, Name),
Builder(StringTableBuilder::RAW, Alignment) {}
void MergeSyntheticSection::addSection(MergeInputSection *MS) {
MS->Parent = this;
Sections.push_back(MS);
}
void MergeSyntheticSection::writeTo(uint8_t *Buf) { Builder.write(Buf); }
bool MergeSyntheticSection::shouldTailMerge() const {
return (this->Flags & SHF_STRINGS) && Config->Optimize >= 2;
}
void MergeSyntheticSection::finalizeTailMerge() {
// Add all string pieces to the string table builder to create section
// contents.
for (MergeInputSection *Sec : Sections)
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Builder.add(Sec->getData(I));
// Fix the string table content. After this, the contents will never change.
Builder.finalize();
// finalize() fixed tail-optimized strings, so we can now get
// offsets of strings. Get an offset for each string and save it
// to a corresponding StringPiece for easy access.
for (MergeInputSection *Sec : Sections)
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
}
void MergeSyntheticSection::finalizeNoTailMerge() {
// Add all string pieces to the string table builder to create section
// contents. Because we are not tail-optimizing, offsets of strings are
// fixed when they are added to the builder (string table builder contains
// a hash table from strings to offsets).
for (MergeInputSection *Sec : Sections)
for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
if (Sec->Pieces[I].Live)
Sec->Pieces[I].OutputOff = Builder.add(Sec->getData(I));
Builder.finalizeInOrder();
}
void MergeSyntheticSection::finalizeContents() {
if (shouldTailMerge())
finalizeTailMerge();
else
finalizeNoTailMerge();
}
size_t MergeSyntheticSection::getSize() const { return Builder.getSize(); }
// This function decompresses compressed sections and scans over the input
// sections to create mergeable synthetic sections. It removes
// MergeInputSections from the input section array and adds new synthetic
// sections at the location of the first input section that it replaces. It then
// finalizes each synthetic section in order to compute an output offset for
// each piece of each input section.
void elf::decompressAndMergeSections() {
// splitIntoPieces needs to be called on each MergeInputSection before calling
// finalizeContents(). Do that first.
parallelForEach(InputSections, [](InputSectionBase *S) {
if (!S->Live)
return;
if (Decompressor::isCompressedELFSection(S->Flags, S->Name))
S->uncompress();
if (auto *MS = dyn_cast<MergeInputSection>(S))
MS->splitIntoPieces();
});
std::vector<MergeSyntheticSection *> MergeSections;
for (InputSectionBase *&S : InputSections) {
MergeInputSection *MS = dyn_cast<MergeInputSection>(S);
if (!MS)
continue;
// We do not want to handle sections that are not alive, so just remove
// them instead of trying to merge.
if (!MS->Live)
continue;
StringRef OutsecName = getOutputSectionName(MS->Name);
uint32_t Alignment = std::max<uint32_t>(MS->Alignment, MS->Entsize);
auto I = llvm::find_if(MergeSections, [=](MergeSyntheticSection *Sec) {
return Sec->Name == OutsecName && Sec->Flags == MS->Flags &&
Sec->Alignment == Alignment;
});
if (I == MergeSections.end()) {
MergeSyntheticSection *Syn = make<MergeSyntheticSection>(
OutsecName, MS->Type, MS->Flags, Alignment);
MergeSections.push_back(Syn);
I = std::prev(MergeSections.end());
S = Syn;
} else {
S = nullptr;
}
(*I)->addSection(MS);
}
for (auto *MS : MergeSections)
MS->finalizeContents();
std::vector<InputSectionBase *> &V = InputSections;
V.erase(std::remove(V.begin(), V.end(), nullptr), V.end());
}
MipsRldMapSection::MipsRldMapSection()
: SyntheticSection(SHF_ALLOC | SHF_WRITE, SHT_PROGBITS, Config->Wordsize,
".rld_map") {}
ARMExidxSentinelSection::ARMExidxSentinelSection()
: SyntheticSection(SHF_ALLOC | SHF_LINK_ORDER, SHT_ARM_EXIDX,
Config->Wordsize, ".ARM.exidx") {}
// Write a terminating sentinel entry to the end of the .ARM.exidx table.
// This section will have been sorted last in the .ARM.exidx table.
// This table entry will have the form:
// | PREL31 upper bound of code that has exception tables | EXIDX_CANTUNWIND |
// The sentinel must have the PREL31 value of an address higher than any
// address described by any other table entry.
void ARMExidxSentinelSection::writeTo(uint8_t *Buf) {
// The Sections are sorted in order of ascending PREL31 address with the
// sentinel last. We need to find the InputSection that precedes the
// sentinel. By construction the Sentinel is in the last
// InputSectionDescription as the InputSection that precedes it.
OutputSection *C = getParent();
auto ISD = std::find_if(C->Commands.rbegin(), C->Commands.rend(),
[](const BaseCommand *Base) {
return isa<InputSectionDescription>(Base);
});
auto L = cast<InputSectionDescription>(*ISD);
InputSection *Highest = L->Sections[L->Sections.size() - 2];
InputSection *LS = Highest->getLinkOrderDep();
uint64_t S = LS->getParent()->Addr + LS->getOffset(LS->getSize());
uint64_t P = getVA();
Target->relocateOne(Buf, R_ARM_PREL31, S - P);
write32le(Buf + 4, 0x1);
}
ThunkSection::ThunkSection(OutputSection *OS, uint64_t Off)
: SyntheticSection(SHF_ALLOC | SHF_EXECINSTR, SHT_PROGBITS,
Config->Wordsize, ".text.thunk") {
this->Parent = OS;
this->OutSecOff = Off;
}
void ThunkSection::addThunk(Thunk *T) {
uint64_t Off = alignTo(Size, T->Alignment);
T->Offset = Off;
Thunks.push_back(T);
T->addSymbols(*this);
Size = Off + T->size();
}
void ThunkSection::writeTo(uint8_t *Buf) {
for (const Thunk *T : Thunks)
T->writeTo(Buf + T->Offset, *this);
}
InputSection *ThunkSection::getTargetInputSection() const {
const Thunk *T = Thunks.front();
return T->getTargetInputSection();
}
InputSection *InX::ARMAttributes;
BssSection *InX::Bss;
BssSection *InX::BssRelRo;
BuildIdSection *InX::BuildId;
InputSection *InX::Common;
SyntheticSection *InX::Dynamic;
StringTableSection *InX::DynStrTab;
SymbolTableBaseSection *InX::DynSymTab;
InputSection *InX::Interp;
GdbIndexSection *InX::GdbIndex;
GotSection *InX::Got;
GotPltSection *InX::GotPlt;
GnuHashTableSection *InX::GnuHashTab;
IgotPltSection *InX::IgotPlt;
MipsGotSection *InX::MipsGot;
MipsRldMapSection *InX::MipsRldMap;
PltSection *InX::Plt;
PltSection *InX::Iplt;
StringTableSection *InX::ShStrTab;
StringTableSection *InX::StrTab;
SymbolTableBaseSection *InX::SymTab;
template GdbIndexSection *elf::createGdbIndex<ELF32LE>();
template GdbIndexSection *elf::createGdbIndex<ELF32BE>();
template GdbIndexSection *elf::createGdbIndex<ELF64LE>();
template GdbIndexSection *elf::createGdbIndex<ELF64BE>();
template void PltSection::addEntry<ELF32LE>(SymbolBody &Sym);
template void PltSection::addEntry<ELF32BE>(SymbolBody &Sym);
template void PltSection::addEntry<ELF64LE>(SymbolBody &Sym);
template void PltSection::addEntry<ELF64BE>(SymbolBody &Sym);
template InputSection *elf::createCommonSection<ELF32LE>();
template InputSection *elf::createCommonSection<ELF32BE>();
template InputSection *elf::createCommonSection<ELF64LE>();
template InputSection *elf::createCommonSection<ELF64BE>();
template MergeInputSection *elf::createCommentSection<ELF32LE>();
template MergeInputSection *elf::createCommentSection<ELF32BE>();
template MergeInputSection *elf::createCommentSection<ELF64LE>();
template MergeInputSection *elf::createCommentSection<ELF64BE>();
template class elf::MipsAbiFlagsSection<ELF32LE>;
template class elf::MipsAbiFlagsSection<ELF32BE>;
template class elf::MipsAbiFlagsSection<ELF64LE>;
template class elf::MipsAbiFlagsSection<ELF64BE>;
template class elf::MipsOptionsSection<ELF32LE>;
template class elf::MipsOptionsSection<ELF32BE>;
template class elf::MipsOptionsSection<ELF64LE>;
template class elf::MipsOptionsSection<ELF64BE>;
template class elf::MipsReginfoSection<ELF32LE>;
template class elf::MipsReginfoSection<ELF32BE>;
template class elf::MipsReginfoSection<ELF64LE>;
template class elf::MipsReginfoSection<ELF64BE>;
template class elf::DynamicSection<ELF32LE>;
template class elf::DynamicSection<ELF32BE>;
template class elf::DynamicSection<ELF64LE>;
template class elf::DynamicSection<ELF64BE>;
template class elf::RelocationSection<ELF32LE>;
template class elf::RelocationSection<ELF32BE>;
template class elf::RelocationSection<ELF64LE>;
template class elf::RelocationSection<ELF64BE>;
template class elf::SymbolTableSection<ELF32LE>;
template class elf::SymbolTableSection<ELF32BE>;
template class elf::SymbolTableSection<ELF64LE>;
template class elf::SymbolTableSection<ELF64BE>;
template class elf::HashTableSection<ELF32LE>;
template class elf::HashTableSection<ELF32BE>;
template class elf::HashTableSection<ELF64LE>;
template class elf::HashTableSection<ELF64BE>;
template class elf::EhFrameHeader<ELF32LE>;
template class elf::EhFrameHeader<ELF32BE>;
template class elf::EhFrameHeader<ELF64LE>;
template class elf::EhFrameHeader<ELF64BE>;
template class elf::VersionTableSection<ELF32LE>;
template class elf::VersionTableSection<ELF32BE>;
template class elf::VersionTableSection<ELF64LE>;
template class elf::VersionTableSection<ELF64BE>;
template class elf::VersionNeedSection<ELF32LE>;
template class elf::VersionNeedSection<ELF32BE>;
template class elf::VersionNeedSection<ELF64LE>;
template class elf::VersionNeedSection<ELF64BE>;
template class elf::VersionDefinitionSection<ELF32LE>;
template class elf::VersionDefinitionSection<ELF32BE>;
template class elf::VersionDefinitionSection<ELF64LE>;
template class elf::VersionDefinitionSection<ELF64BE>;
template class elf::EhFrameSection<ELF32LE>;
template class elf::EhFrameSection<ELF32BE>;
template class elf::EhFrameSection<ELF64LE>;
template class elf::EhFrameSection<ELF64BE>;
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